Copper nugget weighing several tons found near Coloma, WI. (Photo by W. Cordua)

Formula: Cu Isometric


Copper wire on gossan, Flambeau Mine, Ladysmith, Rusk County, WI. The wires are a few mm long. (Photograph and specimen by Pete Rodewald)

Native copper occurs as veins and cavity fillings in hydrothermally altered basaltic igneous rocks. It is also a product of near-surface supergene alteration of other copper minerals, such as chalcopyrite. Copper can survive weathering, although its surface is often coated with green or black weathering rinds consisting of malachite, azurite, cuprite and other minerals. Major copper deposits occur in the Upper Peninsula of Michigan in Keweenawan basaltic lava and interlayered sediments formed approximately a billion years ago. Similar but much smaller deposits are known where these rocks extend into Wisconsin through Bayfield, Washburn, Douglas and Polk counties. Nuggets of copper weighing anywhere from a fraction of an ounce up to 6000 lbs. have been found in glacial drift derived from the weathering of this bedrock (Salisbury, 1985). Although Salisbury further states “specimens of 40 to 50 lbs, weight are not uncommon”, this author has found that nuggets that size are far from common. Such “drift copper” can turn up anywhere in the state and is easily recognized by its bright green to black alteration crust, high density, malleability and brilliant copper color on a fresh surface.

Sukow (1987) notes that many pinkish Lake Superior agates contain tiny platy to arborescent copper inclusions. The copper may be dispersed or oriented along certain layers within the agate. These copper inclusions can often be seen with a hand lens. Associated bornite, malachite and cuprite may also occur in the agate.

ASHLAND COUNTY: Salisbury (1885) reports the find of a 100 lb copper boulder from Outer Island. Eckert (1987) reports copper from Copper Falls State Park. Several small mines were worked in the area for shows of copper. These include the Barabe Mine (SE SE sec. 32 T.45N R3W), the Bayfield Mine, (NW sec. 6 T.44N. R.5W. and the Holmes prospect (sec. 34 T.45N. R.2W) (Cox, 2002).

BAYFIELD COUNTY: A float copper boulder weighing 1,700 lbs. was found in the bed of the Sioux River about 6 miles south of Lake Superior (Salisbury, 1885).
— Native copper occurs in number of small pits and shafts collectively called the Montrose locality in the NW NW Sec. 12 T.44N R.9W near Upper Eau Claire Lake. The native copper is in amygdule in basalt, as well as in breccias and conglomerate. Epidote, calcite, quartz, prehnite and laumontite are also found at this locality (Grant, 1901).

DANE COUNTY: A 30 lb. nugget of drift copper was found in a 20 foot deep well in Madison (Salisbury, 1885).

DOUGLAS COUNTY: Many copper localities are known in the Keweenawan basaltic rocks of this county. Residents in the late 19th and early 20th centuries had great hopes that the region would become a major copper mining district similar to that in Michigan. Such a boom never occurred, as the known deposits are too small or sporadic to warrant serious development. The mines do furnish some interesting mineral collecting even though they are often hard to find in the brush that has grown up in the decades since they were abandoned.
— One of the larger copper developments was the Weyerhauser Mine, a series of shafts and small dumps in the NW SE Sec. 12 (shafts #1, 2 and 3) and in the SE SE Sec. 11 (F shaft) T.43N R.10W near Gordon. The F shaft descended 300 feet and had 4 levels. The native copper is found as small wires and masses in veins and amygdales in basaltic lava flows. One mass reportedly weighed 7 lbs. Prehnite, epidote, calcite, quartz, chlorite, bornite, malachite, azurite, and silver are associated minerals. (Smith, 1947; White, 1978).
— Copper is reported with epidote in basalts at the Williams property (SE SW Sec. 28 T.43N R.10W) north of Hayward (Grant, 1901).
— Copper occurs at the Superior Copper Mine in the NW Sec. 6 T.43N R.13W, east of Dairyland (Mengel, 1971).
— Copper is found with epidote in basalt along Crotty Creek in the NW Sec. 7 T.43N R.13W. 3 small pits were dug here at Copper Mine Dam. Copper is also found along Crotty Creek in amygdales in basalt with prehnite in the center of Sec. 30 T.44N R.13W (Grant, 1901).
— Copper is found with epidote as “specks” in the SE NE Sec. 14 T.44N R.13W at the Arnold prospect, near Solon Springs (Grant, 1901; Mengel, 1971). Grant also reports copper in basalt with quartz, calcite, epidote and chlorite outcropping near by on the west branch of Moose River.
— Copper occurs at the Nowell prospect in the SE 1/4 Sec. 34 T.44N R.14W (Mengel, 1971).
— Copper occurs at the Chippewa and North Wisconsin copper properties located along the Middle River in the SW SW Sec. 3 and NW Sec. 10 T.47N R.12W. The copper occurs in veins and amygdules in basalt with chlorite, prehnite, epidote, quartz and laumontite (Holliday, 1955).
— Copper occurs at the Houghton prospect in Sec. 4 and at the Badger prospect in the NE 1/4 Sec. 8 T.47N R.12W near Rockmont (Mengel, 1971).
— Copper occurs at the Copper King prospect in the SW Sec. 10 T.47N R.12W west of Poplar (Mengel, 1971).
— Copper at the Wisconsin Mine (Edwards Mine) NE SE Sec. 2 T.47N R.13W occurred as “shot and nugget” ore with copper masses weighing 1-15 lbs. Associated minerals are prehnite, calcite, quartz and epidote (Sweet, 1880).
— Copper occurs in a brecciated zone and in amygdules in basalt at the Starkweather mine in the NW NW Sec. 2 T.47N R.13W south of South Range (Dutton, 1972).
— Copper is locally abundant, sometimes as sheets up to 1/8 inch thick at the Fond du Lac mine in the SE NE Sec. 8 T.47N R. 13W. A number of pits and trenches have been dug at this locality. Other minerals found include prehnite, quartz, epidote and calcite (Grant, 1901).
— Copper is found at the Amnicon copper prospect in the NE NW Sec. 11 T.47N R.13W south of the South Range. The copper is in veins and amygdules with quartz, calcite, chalcopyrite and chalcocite (Grant, 1901).
— Copper is found in veins, amygdules and breccia zones in pits at Copper Creek in the SW Sec. 14 and SE Sec. 15 T.47N R.14W. The locality is within Pattison State Park. Quartz, calcite, prehnite and laumontite are also reported (Sweet, 1880; Grant, 1901; Dutton, 1972).
— Copper also occurs with malachite and quartz at the Culligan prospect pits in the SW Sec. 29, SE Sec. 30 and NE Sec. 31 T.47N R.14W southwest of Pattison State Park (Grant, 1901; Dutton, 1972).
— Copper occurs at the Percival Jr. prospect in the SW NE Sec. 24 T.47N R.10W south of Waino. The copper is disseminated through basaltic rock as well as in amygdules. Epidote, prehnite and laumontite also occur here (Dutton, 1972; Mengel, 1971; Grant, 1901).
— Copper is found as masses and nuggets weighing up to 7 lbs. in calcite veins at the Percival copper prospect in the N1/2 SW NE sec. 27 T.48N R.10W. The veins cross-cut amygdaloidal basalt. Prehnite, laumontite and epidote are also found here (Grant, 1901; Sweet, 1880).
— Small copper pits are found in the NW Sec. 28 and the NE Sec. 29 T.48N R.10W near Blueberry. Here small amounts of copper were found in basaltic volcanic rocks with epidote and chalcopyrite (Grant, 1901).
— Sparse copper is found at the Catlin locality in SE Sec. 34 T.48N. R.13W south of South Range (Dutton, 1972).

DODGE COUNTY: A nugget of float copper weighing 487 lbs. was found near Hustiford (Irving, 1882).

FOREST COUNTY: Copper occurs in the oxidized zone of the Crandon massive sulfide deposit near Little Sand Lake. Samples found in core from the proposed production shaft contained native copper along bedding and fractures in chlorite schist. The copper was in “fine dendrites attaining the length of several centimeters”. (Erickson and Cote, 1996).

IRON COUNTY: Copper is found in veins cutting amygdaloidal basalts with calcite and laumontite along the Montreal River gorge in Sec. 21 T.47N R.1E (Irving, 1883).
— A few crystals of native copper were collected from the iron formation exposed in the Cary Mine in Hurley (Dickson, 1938).
—The Vogel prospect was a small working for copper in the late 1800’s in sec. 6 T.45N. R.1E. (Cox, 2002).

JEFFERSON COUNTY: Salisbury(1885) reports copper along bedding planes in limestone in a quarry near Lake Koshkonong.

LAFAYETTE COUNTY: Copper is reported as a rare secondary mineral in the zinc-lead ores in the Belmont and Calamine districts (Klemic and West, 1964).
— Heyl et al. (1959) report copper as an oxidation product associated with other copper minerals in Sec. 36 T.2N R.3E approximately 4 miles N.W. of Gratiot.

MARQUETTE COUNTY: A mass of native copper, with a weight estimated at 6,000 – 8,000 lbs was found in float at the quarry run by Krammer and Sons at Glover Bluff, sec. 3, T18N R8E.

PIERCE COUNTY: A nugget weighing 15 lbs. was plowed up in a farm field near Ellsworth. Numerous other nuggets weighing more than a pound have been found in the glacial drift in the county. (WSC., 1990).

POLK COUNTY: Copper occurs rarely as thin films and masses up to several kilograms in the amygdaloidal basalts at Sec. 5 and 6 T.33N R.18W at the Dresser Trap Rock Quarry (Cordon, 1989b).
— Shows of native copper associated with cuprite, chalcocite and malachite are reported in the Fredrick-Clam Falls area (Hansell, 1928 a and b). Some localities are: in breccia in a small test pit in the NE SE Sec. 10 T.39N R.17W.;SE SE NW Sec. 18 T.37N R.16W; SE SW Sec. 21 T.37N R.16W; NE SW Sec. 23 T.37N R.16W; and NW NW Sec. 35 T.37N R.14W.

ROCK COUNTY: A 114 lb. nugget of drift copper was found near Newark (Salisbury, 1885).

RUSK COUNTY: Copper occurs in the oxidized-supergene zone of the Flambeau Mine (sec. 9 T.34N. R.6W.) near Ladysmith. It forms foil and flake coatings on joints and as sheets 1-3mm thick and over 10 cm. long sometimes associated with silver. It as forms delicate wires and micro-crystal clusters dominated by {100} and {111} combinations, in altered metachert. The copper is unusually rich in mercury (0.11 weight %) (May,1977, Rosemeyer, 1997; Motti, et al., 1999)

SHAWANO COUNTY: A 970 lb. mass of drift copper was found in a gravel pit 2 miles south of Pella (WGNHS files).

WASHBURN COUNTY: Copper in brecciated and epidotized basalt and in thin conglomerate is found at the Mudge prospect in the NE 1/4 Sec. 5 T.42N R.10W, northwest of Chittamo. Small nuggets up to 5 cm. long have been reported. Quartz, calcite, prehnite and malachite also appear (Grant, 1901).

WALWORTH COUNTY: A 40 to 50 lb. boulder of drift copper was found near State Line (Salisbury, 1885).

WAUSHARA COUNTY: An enormous boulder of drift copper, estimated to weigh between 3 and 4 tons was in a pit near Coloma by workers of the Ed. Kraemer and sons company.